To gain weight actually means to gain fat. For an adult who has stopped growing and developing, as long as the energy intake is greater than the consumption, the excess energy is converted into fat and stored to grow fat. The reasoning is understood, so eat less. In fact, some people do not eat less, such as dinner without rice, soon hungry, so eat 2 two French fries, calories far more than half a pound of rice. Even if you eat less, consumption is also reduced, there is still excess energy. So, the daily activities are similar, why the consumption will be reduced? This is the problem of “basal metabolic rate”, which is the amount of energy you will consume even if you lie in bed all day and do nothing. Basal metabolic rate varies with gender and age. Men’s basal metabolic rate is higher than women’s, and it is highest in infancy and gradually decreases with age. This is why it is often the case that women who were slim in their youth become fat in middle age. Generally speaking, the difference between the basal metabolic rate and the normal value within 10%-15% is normal. In hyperthyroidism, the basal metabolic rate increases by 25% to 80%, so hyperthyroid patients are often thin. In hypothyroidism, the basal metabolic rate decreases by 20%-40%; in other cases, such as adrenal cortex and pituitary gland hypofunction, the basal metabolic rate will also decrease. Some people who are particularly prone to “gaining weight” may be suffering from hypothyroidism and should go to the hospital for appropriate tests in a timely manner. The basal metabolism accounts for 70% of the body’s calorie consumption, and excessive dieting can cause the basal metabolic rate to drop because organisms have evolved a well-developed self-protection mechanism. Excessive dieting gives the body a signal: energy shortage. It responds by reducing consumption, lowering the basal metabolic rate and increasing fat reserves. The result is an “energy-efficient, fat-prone body” that gets fatter as it loses weight. The way to protect the basal metabolic rate is to moderately reduce the amount of food you eat, especially high-calorie food, but ensure protein intake, maintain a regular diet and sleep, and insist on regular aerobic exercise to increase body muscle mass and burn off excess energy.